ArticlePDF Available

Pantydraco n. gen. for Thecodontosaurus caducus YATES, 2003, a basal sauropodomorph dinosaur from the Upper Triassic or Lower Jurassic of South Wales, UK

Authors:

Abstract

Numerous isolated bones from a Rhaetian (Upper Triassic) fissure fill in Clifton, Bristol, England have been referred to the basal sauropodomorph Thecodontosaurus Riley & Stutchbury, 1836 (type genus of T. antiquus Riley & Stutchbury vide Owen, 1842). T. caducus Yates, 2003 (Rhaetian or Lower Jurassic fissure fill, South Wales) is based on several articulated partial skeletons of juvenile individuals. T. antiquus is based on the isolated neotype dentary that does not possess an autapomorphy or a unique combination of characters. This dentary is unusually short and deep but this character is also present in T. caducus and Saturnalia tupiniquim (Upper Triassic, Brazil). However, the characters of referred Clifton postcrania cannot be used to diagnose Thecodontosaurus because there are three humeral morphs from Clifton. No other bones from Clifton have characters diagnostic for T. caducus and the ages of the two fissure fills may be different. The gracile morph, long referred to T. antiquus, is present in the monospecific assemblage of 1000's of isolated sauropomorph bones from the Rhaetian fissure fill at Tytherington Quarry near Bristol. A comprehensive cladistic analysis of basal sauropodomorphs, in which T. antiquus (characters mostly based on Tytherington bones) and T. caducus were included as separate terminal taxa, failed to recover a monophyletic Thecodontosaurus in all of the most parsimonious trees. T. caducus Yates, 2003 is made the type species of Pantydraco n. gen., which can be diagnosed by the autapomorphic presence of pneumatic openings on cervical vertebrae 6-8. The prominent apex of the anteroposteriorly low asymmetrical deltopectoral crest is at 40% of humeral length (versus low at 25 %, and high at 40 % and at + 50 % in Clifton humeri) and the tubercle medial to the head is small (large in Clifton humeri).
A preview of the PDF is not available
... The specimens that have been included as part of the operational taxonomic unit (OTU) of Plateosaurus through time have not been constant. Two matrices with different taxonomic and character compositions were produced in 2007, namely by Upchurch et al. (2007) and Yates (2007) (Fig. 2). These matrices were subsequently modified through eight iterations until 2019. ...
... In Plateosaurus (= 'Sellosaurus') gracilis, it has been recognised that there are two types of sacra: type I, which involves a dorsosacral, primordial sacral 1 and primordial sacral 2, and type II, interpreted as primordial sacral 1, primordial sacral 2 and caudosacral (Galton 1999(Galton , 2000. The differences were interpreted as either evidence of sexual dimorphism (Gal- Figure 2. Iterations on the matrices originally built by Upchurch et al. (2007) and Yates (2007) ton 2000) or homeotic transformation Upchurch 2000, Galton 2001b). Type I (dorsosacral, primordial sacral 1 and primordial sacral 2) is the most common condition among early-diverging sauropodomorphs, as in Ruehleia Galton, 2001b, andEfraasia Galton, 1973, taxa from Germany, and the persistent condition in Massospondylidae (Wang et al. 2017). ...
... Since the character was not illustrated, it is not easy to know what structure this refers to and has been removed. It was initially scored by Yates (2007) for Lufengosaurus Young, 1940 (specimens IVPP V15, andillustrations in Young 1941;Barrett et al. 2005a), Yunnanosaurus huangi Young, 1940 (specimens IVPP V94, V505, and illustrations in Young 1942Young , 1951 and ...
Article
Full-text available
A literature review showed that there is not a defined consensus on what specimens belong to Plateosaurus in current phylogenetic analyses, and after the assignation of SMNS 13200 as the neotype for Plateosaurus, the specimen composition of Plateosaurus as an operational taxonomic unit (OTU) needs to be addressed in further iterations of phylogenetic analyses. At least one of the specimens used to illustrate plateosaurian anatomy contains several characters identified in more derived sauropodomorphs commonly referred to as massopodans. This partial skeleton, traditionally known as specimen ‘GPIT IV’, was found in the lower dinosaur bone bed of the Obere Mühle, a Trossingen Formation outcrop, during an excavation in 1922 near the city of Tübingen, Germany. The holotype of Plateosaurus trossingensis and several other specimens referred to as this species were found in this level, which was initially interpreted as a synchronic deposit of animals. However, the current understanding of the Trossingen Formation indicates that this bed was probably a constant accumulation of carcasses through miring and transport down a river for hundreds of years. In this work, a framework to compare phylogenetic signals with morphological and histological data is provided to help in the species delineation of Plateosaurus, and support is found to refer the historic specimen ‘GPIT IV’ as a new genus and a new species.
... The synapomorphies that are used to diagnose Sauropodomorpha as a clade vary from study to study (Gauthier, 1986;Sereno, 1999a;Langer and Benton, 2006;Baron et al., 2017a). Four major character sets that have been compiled to date, i. e. , Yates, (2007), Pol et al., (2011), and . The apomorphybased definition of Sauropodomorpha has been in constant flux as these datasets produce different results and have been used as the basis for many further analyses (e.g. ...
... The three major datasets most often used to explore early sauropodomorph relationships (i. e., , Yates, 2007 were independent compilations of characters in the literature plus additions from personal observations. This study by Peyre de Fabregues et al. (2015) noted that character choice and character scoring are at the root of the inconsistencies found, however, character scorings are based mostly on the way in which the character states are defined. ...
... Some researchers have leant towards more complete geographic representation of the taxonomic scope to discriminate the best matrix, for example sampled all of the then published sauropodomorphs from Argentina (Martínez, 2009). On the other hand, the recursively modified versions of the dataset of Yates (2007) were built and expanded on the basis that these sample the largest number of characters and taxa (e.g. Apaldetti et al., 2011, McPhee et al., 2014, 2015b, 2015a. ...
Thesis
Full-text available
Non-sauropod sauropodomorphs, also known as 'basal sauropodomorphs' or 'prosauropods', have been thoroughly studied in recent years. Several hypotheses on the interrelationships within this group have been proposed, ranging from a complete paraphyly, where the group represents a grade from basal saurischians to Sauropoda, to a group on its own. The grade-like hypothesis is the most accepted; however, the relationships between the different taxa are not consistent amongst the proposed scenarios. These inconsistencies have been attributed to missing data and unstable (i.e., poorly preserved) taxa, nevertheless, an extensive comparative cladistic analysis has found that these inconsistencies instead come from the character coding and character selection, plus the strategies on merging data sets. Furthermore, a detailed character analysis using information theory and mathematical topology as an approach for character delineation is explored here to operationalise characters and reduce the potential impact of missing data. This analysis also produced the largest and most comprehensive matrix after the reassessment and operationalisation of every character applied to this group far. Additionally, partition analyses performed on this data set have found consistencies in the interrelationships within non-sauropod Sauropodomorpha and has found strong support for smaller clades such as Plateosauridae, Riojasauridae, Anchisauridae, Massospondylinae and Lufengosarinae. The results of these analyses also highlight a different scenario on how quadrupedality evolved, independently originating twice within the group, and provide a better framework to understand the palaeo-biogeography and diversification rate of the first herbivore radiation of dinosaurs.
... In 1975, sauropodomorph material was found in Tytherington, southwest England (Whiteside and Marshall, 2008;Whiteside et al., 2016), and since then it has been housed and prepared at the University of Bristol Geology Department (BRSUG). The new Tytherington material was later identified as T. antiquus (Whiteside, 1983;Galton et al., 2007), but it was never formally described. These interpretations and findings complicate the taxonomic status of Thecodontosaurus and apparently increase the number of sauropodomorph taxa that lived in southwestern Britain during the Late Triassic. ...
... The deltopectoral crest extends for ca. 43°of the length of the humerus, similar to the condition in most basal sauropodomorphs (Galton, 1973;Langer, 2003;Pol et al., 2011;Sereno et al., 2013;McPhee et al., 2019), including the Durdham Down T. antiquus and YPM 2195 (Benton et al., 2000;Galton et al., 2007). Galton (2007) noted that the deltopectoral crest of YPM 2195 had a rounded apex at 25°of the humeral length, proposing it to be an autapomorphy of Asylosaurus that distinguished it from the rest of the Durdham Down humeri, although this crest is incomplete in these specimens. ...
... Ilium-Tytherington has yielded a number of Thecodontosaurus ilia, three of which are almost complete, enabling the accurate reconstruction of this element (Fig. 9). The ilium is anteroposteriorly longer than dorsoventrally tall, with a height-to-length (from the anterior end of the pubic peduncle to the posterior end of the postacetabular process) ratio of 54%, similar to that of Panphagia (52%; Martínez and Alcober, 2009) and proportionally more elongated than those of Chromogisaurus (61%; Ezcurra, 2010), Saturnalia (62%; Langer, 2003), and particularly Buriolestes (67%; Cabreira et al., 2016) and Pantydraco (68%; Galton et al., 2007;Galton and Kermack, 2010). The dorsal outline, complete in BRSUG 28121, is almost straight in lateral view. ...
Article
Full-text available
Thecodontosaurus antiquus is a basal sauropodomorph from the Rhaetian locality of Durdham Down in Bristol, U.K. Sauropodomorph material putatively assigned to this species was found at the nearby site of Tytherington. Here, we describe the Tytherington specimens and compare them with T. antiquus and other Late Triassic sauropodomorphs from Britain. We find that this material can be assigned to T. antiquus based on multiple shared morphological traits, and we provide a revised diagnosis of this taxon. The new anatomical information from the Tytherington specimens enriches the osteology of the species, particularly of previously unknown parts of the skeleton such as the skull. We find poor anatomical support to distinguish the contemporary Pantydraco caducus from T. antiquus, such that the former might represent a juvenile of the latter. We also discuss the questionable validity of Asylosaurus yalensis. Thecodontosaurus antiquus is one of the most basal sauropodomorphs that show craniodental traits related to herbivory, while retaining a plesiomorphic limb morphology and posture. This taxon was an important component of Rhaetian insular ecosystems of southwestern Britain.
... A few specimens are still indeterminate to date, but most of them have been assigned to new or already existing genera. Non-sauropodan sauropodomorph juveniles attributed to six different genera, as well as one indeterminate specimen, were reported from Upper Triassic deposits: Efraasia (Galton and Bakker, 1985), Thecodontosaurus (Benton et al., 2000), Euskelosaurus (Durand, 2001), Mussaurus (Pol and Powell, 2007;Cerda et al., 2014), Pantydraco (Galton et al., 2007;Galton and Kermack, 2010), Plateosaurus (Hofmann and Sander, 2014), and MMACR-PV-028-T (Pretto et al., 2016). ...
Article
An incomplete dinosaur skeleton, including a partial skull, recently discovered from the Lower Jurassic Lufeng Formation of Yunnan, China, is here described. Except for its small size, little anatomical evidence supports, a priori, the non‐adult status of this new sauropodomorph specimen. Thus, osteohistological analyses were conducted, which suggest that the new specimen is a fast‐growing juvenile. Despite the abundant early sauropodomorph fossils collected from the Lufeng Formation, it represents only the second occurrence of a juvenile non‐sauropodan sauropodomorph in the Lufeng Basin. The anatomy of the specimen does not match that of other Lower Jurassic immature specimens. Although cranial material is preserved, it does not display diagnostic characters of the early sauropodomorphs from the same horizon, namely Lufengosaurus, Yizhousaurus and Yunnanosaurus. Our phylogenetic analysis, which places the new specimen in a position relatively distant to other Chinese sauropodomorphs, corroborates the systematic hypothesis indicated by the anatomical evidence that it is not referable to a species already excavated in Yunnan. However, this result should be interpreted with caution considering that ontogeny affects phylogenetic reconstruction. A thorough comparison with adult forms, taking into account ontogeny‐related characters, suggests that this new juvenile specimen could represent an unknown species of early sauropodomorph.
... In instances of deformation, we used Maya's lattice deform tool to retro-deform a bone to conform to the shape of its less deformed counterpart on the opposite side of the individual in order to maximize the completeness of the composite bone. Retrodeformation was applied taking into account previous guidelines (Tschopp et (Galton et al. 2007). The missing margins of the maxillae, premaxillae, and mandibles, which were lost due to overpreparation, are based on the position of the boundary between the tooth roots and crowns when the teeth are set at their maximum depth in their respective sockets. ...
Article
Full-text available
Sauropod dinosaurs include the largest terrestrial vertebrates that have ever lived. Virtually every part of the sauropod body is heavily modified in association with gigantic size and associated physiological alterations. Sauropod skulls are no exception: they feature elongated, telescoped facial regions connected to tilted neurocrania and reoriented jaw adductor muscles. Several of these cranial features have been suggested to be adaptations for feeding on the one hand and the result of paedomorphic transformation near the base of Sauropoda on the other. However, the scarcity of sauropodomorph ontogenetic series has impeded further investigation of these hypotheses. We re‐evaluated the cranial material attributed to the early sauropodomorph Anchisaurus, which our phylogenetic analyses confirm to be closely related to sauropods. Digital assembly of μCT scanned skulls of the two known specimens, a juvenile and an adult, permitted us to examine the detailed ontogeny of cranial elements. The skull anatomy of Anchisaurus is distinguished by a mosaic of ancestral saurischian and sauropod‐like characters. Sauropod‐like characters of the braincase and adductor chamber appear late in ontogeny, suggesting that these features first evolved by the developmental mechanism of terminal addition. Shape analyses and investigation of allometric evolution demonstrate that cranial characters that appear late in the ontogeny of sauropodomorphs closely related to sauropods are already present in the embryos and juveniles of sauropods, suggesting a predisplacement‐type shift in developmental timing from the ancestral anchisaurian condition. We propose that this developmental shift relaxed prior constraints on skull morphology, allowing sauropods to explore a novel range of phenotypes and enabling specializations of the feeding apparatus. The shift in timing occurred in concert with the evolution of gigantism and physiological and locomotory innovations.
... Slightly older taxa, from the Late Triassic (Rhaetian), include a theropod dentary, ?Megalosaurus cambrensis, from south Wales (Newton, 1899;Galton, 2005); an incomplete melanorosaurid sauropodomorph skeleton, Camelotia borealis, from the Penarth Group of Somerset in south-west England (Galton, 1985); various taxonomically indeterminate fragments from the Westbury Formation of Newark, Nottinghamshire (Martill and Dawn, 1986) and Aust Cliff, near Bristol (Storrs, 1994); and the basal sauropodomorphs Thecodontosaurus and Pantydraco from supposedly Rhaetian fissure fills in south-west England and south Wales (Galton et al., 2007;Riley and Stutchbury, 1836;Whiteside et al., 2016). Supposed dinosaur limb bone fragments from the Penarth Group at Aust Cliff, near Bristol (Galton, 2005), are probably jaw fragments from giant ichthyosaurs (Lomax et al., 2018). ...
Article
Full-text available
Several specimens from the Lias Group (Lower Jurassic) of Northern Ireland have been suspected as dinosaurian in origin. Bone histology and morphology demonstrates that two of these, both from the same locality in Co. Antrim, demonstrably are from dinosaurs. We interpret one as the proximal end of the left femur of a basal thyreophoran ornithischian, and tentatively assign it to cf. Scelidosaurus. The other is the proximal part of the left tibia of an indeterminate neotheropod, perhaps a member of the averostran-line similar to Sarcosaurus, or a megalosauroid. These are the first dinosaur remains reported from anywhere in Ireland and some of the most westerly in Europe, and they are among only a small number of dinosaurs known from the Hettangian Stage. Two additional specimens are no longer considered to be from dinosaurs. We interpret one as a surangular or mandible fragment from a large marine reptile, perhaps an ichthyosaur or pliosaur; the other is a polygonal fragment of Paleocene basalt.
... The dinosauromorphs from western Europe are all found in Rhaetian-aged rocks (Fig. 19) with the exception of Saltopus elginensis Huene (1910), a dinosauriform from the Lossiemouth Sandstone Formation (early Norian) from Scotland (Benton and Walker 2011, Baron et al. 2017b). Some of those are from fissure fill deposits, such as the small sauropodomorphs Thecodontosaurus antiquus Morris (1843) and Asylosaurus yalensis Galton (2007a) near Bristol, England (Benton et al. 2000, Galton 2007a, Ballell et al. 2020 and Pantydraco caducus Galton et al. (2007b) from South Wales. The larger melanorosaurid sauropodomorph Camelotia borealis Galton (1985) is known from the Wedmore Stone near the base of the Westbury Formation (Penarth Group), in Somerset, England (Galton 1985(Galton , 1998. ...
Article
Full-text available
Dinosauromorph specimens from Petrified Forest National Park have been recovered from four major collecting efforts since 1982, including the most recent paleontological inventory of new park lands acquired in 2011. Additionally, an emphasis on understanding the stepwise acquisition of character traits along the dinosaurian lineage has helped identify previously collected specimens in museum collections. Here we briefly describe and use apomorphies to identify 32 additional dinosauromorph specimens found at Petrified Forest National Park, bringing the total number of dinosauromorph specimens presently known from the park to 50, a 600% increase since the year 2000. These specimens are all Norian in age and come from the Blue Mesa Member, Sonsela Member, and Petrified Forest Member of the Chinle Formation. These include the proximal end of a tibia that represents the oldest unambiguous dinosaur specimen from the Chinle Formation. We then contextualize these specimens with the dinosauromorph assemblages from the Norian of Utah, Colorado, New Mexico, and Texas, as well as the Carnian and Norian dinosauromorph assemblages from South America, Africa, and Europe. Despite increased sampling we still find no evidence for sauropodomorph and ornithischian dinosaurs in Western North America. An increase in sampling, combined with the use of apomorphies to identify collected specimens, will continue to improve the global dinosauromorph fossil record that can be used to answer questions on biochronology and the evolutionary history of the avian lineage.
Article
Full-text available
The earliest crocodylomorphs, known as non‐crocodyliform crocodylomorphs, first appeared during the Late Triassic. In contrast to extant crocodylians, which are all semi‐aquatic, early crocodylomorphs represent terrestrial taxa with a fully erect posture and in most cases a small body size. Their gracile skeletons suggest an active mode of life, possibly similar to contemporaneous, bipedal theropod dinosaurs. Despite this remarkable body plan, the postcranial morphology of early crocodylomorphs has rarely been documented in detail, restricting our ability to infer aspects of their functional morphology and evolution. Here, we provide a detailed description of the postcranium of Terrestrisuchus gracilis , a small‐bodied crocodylomorph from the Late Triassic of Pant‐y‐Ffynnon Quarry (southern Wales, UK), including a description of long bone tissues based on histological thin sections. Almost all elements of the postcranial skeleton have been preserved. The skeleton of Terrestrisuchus gracilis is highly gracile, even for a non‐crocodyliform crocodylomorph. Osteological correlates of the appendicular skeleton suggest that Terrestrisuchus gracilis had a digitigrade, quadrupedal posture. A quantitative analysis of limb robustness corroborates that Terrestrisuchus gracilis was a quadruped. Histological analysis suggests that all sampled specimens were skeletally immature and had fast growth at the time of death, as indicated by the lack of an external fundamental system and the predominance of fibrolamellar bone. The bone tissue is similar to that recently described for Saltoposuchus connectens and certain non‐crocodylomorph pseudosuchians, but differs from Hesperosuchus agilis and crocodyliforms, in which parallel‐fibred bone is more prevalent.
Article
Full-text available
The genus Plateosaurus is one of the most challenging aspects of early-diverging sauropodomorph taxonomy, with a total of 29 names and a century of revisions. As a result, nomina dubia have been treatedas synonyms of Plateosaurus trossingensis, adding to the confusion about the extent of morphological variability. Here, we provide a thorough revision of the taxonomy proposed by von Huene as well as the subsequent taxonomic interpretations of Plateosaurus through a complete inventory of the specimens stored in the Palaeontological Collection of Tübingen. We reassess the status of the specimens in the collection and propose that the sauropodomorph-bearing layers are not necessarily monospecific. Most of the original fieldwork documentation has been lost, but we use the taxonomy established by von Huene as a historical reference point to reconstruct what was known at the time. This revised taxonomy of Plateosaurus narrows the genus to three species: Pl. trossingensis, Pl. longiceps, and Pl. gracilis (as a metataxon), and restricts the genera Gresslyosaurus and Pachysaurus to large and robust individuals, as pragmatic decisions aimed to test their affinities to other Late Triassic sauropodomorphs. Future studies should consider not only morphological variability, but also stratigraphy, palaeogeography, and environmental data when delineating species within and outside the Plateosaurus plexus.
Article
Full-text available
We describe a new small-bodied coelophysoid theropod dinosaur, Pendraig milnerae gen. et sp. nov, from the Late Triassic fissure fill deposits of Pant-y-ffynnon in southern Wales. The species is represented by the holotype, consisting of an articulated pelvic girdle, sacrum and posterior dorsal vertebrae, and an associated left femur, and by two referred specimens, comprising an isolated dorsal vertebra and a partial left ischium. Our phylogenetic analysis recovers P. milnerae as a non-coelophysid coelophysoid theropod, representing the first-named unambiguous theropod from the Triassic of the UK. Recently, it has been suggested that Pant-y-ffynnon and other nearby Late Triassic to Early Jurassic fissure fill faunas might have been subjected to insular dwarfism. To test this hypothesis for P. milnerae , we performed an ancestral state reconstruction analysis of body size in early neotheropods. Although our results indicate that a reduced body size is autapomorphic for P. milnerae , some other coelophysoid taxa show a similar size reduction, and there is, therefore, ambiguous evidence to indicate that this species was subjected to dwarfism. Our analyses further indicate that, in contrast with averostran-line neotheropods, which increased in body size during the Triassic, coelophysoids underwent a small body size decrease early in their evolution.
Article
Full-text available
The Dinosauria are not characterized by a sacrum with a dorsosacral plus sacrais 1 and 2 because there are two reptilian sacral vertebrae, a plesiomorphic character for Dinosauria, in Herrerasauridae (Upper Triassic) and some individuals of the prosauropod dinosaur Sellosaurus gracilis (?males). A third sacral vertebra, a caudosacral, is present in other individuals of S. gracilis (?females), some other species of prosauropods, and the "primitive three vertebrae sacrum" of sauropods, but in other prosauropod species the third sacral is a dorsosacral. This vertebrae was probably a caudosacral in the theropods Allosaurus and Dilophosaurus. In Ornithischia the situation is indeterminate.
Article
Full-text available
Five shafts of large long bones of dinosaurs have been found since 1846 in the Rhaetic Bone bed of the Westbury Formation (Upper Triassic) at Aust Cliff near Bristol, Avon, southwestern England. Two bones (1 lost) are Dinosauria incertae sedis and a third (also lost), the longest and best preserved, was probably part of a femur of the melanorosaurid prosauropod Camelotia (Upper Triassic, England). The width of the other two femoral shafts is greater transversely than anteroposteriorly, as in Camelotia. However, these shafts are also straight in lateral view, a derived character that occurs only in sauropods and stegosaurs and some Cretaceous ankylosaurs and ornithopods. However, the shafts are curved in lateral view in basal ankylosaurs and Jurassic ornithopods. Unlike the femora of Upper Jurassic sauropods and stegosaurs, in which the bone is almost solid, the Aust shafts consist of a thin layer of compact cortical bone surrounding a large area, most of which is filled with very lightly constructed cancellous bone. However, cross-sections of the humerus just below the deltopectoral crest of the sauropod Isanosaurus (Upper Triassic, Thailand) and the stegosaur Dacentrurus (Upper Jurassic, England) are intermediate in their histology. The femoral shaft is hollow in some Jurassic stegosaurs, though not to the degree shown by those from Aust. The Aust shafts are truly columnar, agreeing with those of stegosaurs in the apparent lack of a prominent fourth trochanter and of the associated posteromedial depression, structures which are prominent in sauropods. These two shafts, with estimated femoral lengths of about 1000-1100 mm, are tentatively referred to the Stegosauria so stegosaurs probably reached a large size in the Upper Triassic ; the earliest definitive record of the group is Middle Jurassic (Bathonian) of England.
Article
Full-text available
The skull and lower jaw of a new sphenodontid reptile Diphydontosaurus avonis is described from disarticulated bones. The fossils were recovered from a detrital limestone of Rhaetian age deposited within solutional and tectonically formed fissures within the Carboniferous Limestone of Tytherington quarry near Bristol. The bone remains, numbering over 1000, are exquisitely preserved with intact facets. Diphydontosaurus was the smallest member of an insular fauna, was primarily insectivorous, and probably formed locally high-density populations. Uniquely for a sphenodontid, Diphydontosaurus had pleurodont teeth on the premaxilla and on the anterior regions of the dentary and maxilla. However, Diphydontosaurus also has the series of acrodont teeth alternating in size on the maxilla and dentary which is characteristic of the Sphenodontidae and particularly Sphenodon. An analysis of 49 synapomorphs in the Diapsida emphasises the sphenodontid nature of Diphydontosaurus. A study of these synapomorphs among the other Triassic sphenodontids Clevosaurus and Planocephalosaurus and the eosuchian Gephyrosaurus suggests that the lack of a quadrate-quadratojugal conch and the complete lower temporal bar are secondarily derived in the `living fossil' Sphenodon punctatus. The tuatara is therefore much less archaic than hitherto proposed. Functional reasons are advocated for the loss of the conch and the regrowth of a complete lower temporal bar. Transformation series are described which could have led to the shape of the maxilla, dentary, premaxilla, palatine and to the loss of the lacrimal in Sphenodon.
Article
Full-text available
Re-examination of the surviving specimens of Thecodontosaurus antiquus indicates that this plesiomorphic sauropodomorph can be diagnosed on the basis of elongate basipterygoid processes, a relatively short dentary, and a squared posterior process of the ilium. Although much of the original topotype material found in the 1830s in Bristol, England, has now been lost, some 245 specimens remain. These indicate a small, gracile prosauropod, up to 2.5 m in length, distinguished primarily on the absence of derived characters seen in other prosauropods. Although attempts were formerly made to subdivide the Bristol specimens into several dinosaurian, and other, taxa, most appear to pertain to the prosauropod Thecodontosaurus antiquus. The specimens do indicate a clear separation into two morphs, a gracile and a robust form, presumably evidence of sexual dimorphism. A juvenile Thecodontosaurus sp. from South Wales may belong to the same species. A cladistic analysis indicates that Prosauropoda is probably a clade, rather than a series of outgroups to Sauropoda, but support for this conclusion is weak. Echoing other recent cladistic analyses, stronger support is found for the existence of a clade Sauropodomorpha, made up from Prosauropoda 1 Sauropoda, for the clade Sauropoda itself, and for the clade Eusauropoda within Sauropoda.
Article
The holotype of the large prosauropod Camelotia borealis GALTON from the basal Westbury Formation (Rhaetic, Upper Triassic) of Wedmore, Somerset, England is illustrated in detail. The femur has two synapomorphic characters of the Melanorosauridae, the lesser trochanter of the femur is sheet-like and the transverse width of the shaft at mid-length is greater than the antero-posterior width. The centra of the most anterior caudal vertebrae are tall but short, as in Melanorosaurus HAUGHTON (Upper Triassic, South Africa), the probable sister group of Camelotia. These characters also show that Camelotia borealis is not a junior synonym of Plateosaurus engelhardti MEYER, the common large plateosaurid from the Upper Triassic of western Europe. The associated teeth of Avalonianus KUHN are referred to the possible carnosaurian theropod ?Megalosaurus cambrensis NEWTON.
Article
The recognition of what are now commonly termed the Dinosauria, as a peculiar group of the Reptilia, is due to that remarkable man whose recent death all who are interested in the progress of sound palæeontology must deplore–Hermann von Meyer. In his ‘Palælogiea,’ published so long ago as 1832 ∗, Von Meyer classifies fossil reptiles according to the nature of their locomotive organs; and his second division, defined as “ Saurians, with limbs like those of the heavy terrestrial Mammalia,” is established for Megalosaurus and Iguanodon. To this group Von Meyer subsequently applied the name of Pachypodes or Pachypoda. Nine years afterwards Professor Owen, in his “Report on British Fossil Reptilia,” conferred a new name upon the group, and attempted to give it a closer definition, in the following passages :– “ Dinosaurians.–This group, which includes at least three well established genera of Saurians, is characterized by a large sacrum composed of five ankylosed vertebræ of unusual construction, by the height and breadth and outward sculpturing of the neural arches of the dorsal vertebræ, by the twofold articulation of the ribs to the vertebræ, viz. at the anterior part of the spine by a head and tuberele, and along the rest of the trunk by a tuberele attached to the transverse process only; by broad and sometimes complicated coracoids and long and slender clavicles, whereby Croeodilian characters of the vertebral column are combined with a Lacertian type of the pectoral arch ; the dental organs also exhibit the same transitional
Article
Extract The fossil remains, described in this paper, were found in quarrying the brecciated beds, which rest upon the highly-inclined carboniferous limestone at Redland, the south-eastern extremity of Durdham Downs, near Bristol. The breccia at this spot is not more than twenty feet thick, and is composed of angular or slightly worn fragments of mountain limestone, cemented by a red or yellow magnesian paste.* It occurs in patches over the whole of the Downs, filling up the hollows and irregularities in the limestone; and it is exhibited in the parishes of Westbury and Henbury, in Gloucestershire, and St. George’s in Somersetshire ; it forms likewise the well-known precipitous cliffs and interesting sections at Hungroad, on the Avon ; and is exhibited in the valley of the Trim, as well as at other places. It is desirable to repeat the observation of Dr. Buckland and Mr. Conybeare, that wherever the breccia occurs in the neighbourhood of Bristol, it is principally composed of the debris of the rocks on which it rests. The whole of the bones were evidently dislocated before they were entombed, as several of the specimens were found in actual contact with the mountain limestone, while others were dispersed throughout the breccia : many of the bones were also clearly fractured before they were enclosed. This deposit has been considered the representative of the lower divisions of the new red sandstone series of Yorkshire and the adjacent counties; and to be in the place of a great part of the
Article
The species taxonomy of the sauropodomorph dinosaurs from the Löwenstein Formation of Germany is examined. Previous work has classified these into two taxa: Sellosaurus gracilis from a number of localities and the widespread Plateosaurus engelhardti from a single monospecific accumulation in the Löwenstein Formation, near the town of Trossingen. The current hypodigm of Sellosaurus gracilis is found to contain a substantial amount of variation. This includes differences in the dentition, structure of the skull, composition of the sacrum and the structure of the caudal vertebrae and pelvis. This variation was analysed using a specimen–based parsimony analysis of the sauropodomorphs from the Löwenstein Formation. It was found that two discrete taxa comprise the current hypodigm of Sellosaurus. The more common of these two is a plesiomorphic form for which the correct name is Efraasia minor comb. nov. The less common form (which includes the holotype of Sellosaurus gracilis) is found to share a number of synapomorphies with Plateosaurus engelhardti and is placed in this genus as Plateosaurus gracilis